Combine harvesters generally include a sieve in the form of a generally horizontal apertured plate which allows the grain to pass through the apertures while the lighter chaff is discharged rearwardly from the sieve. In order to assist the rearward movement of the chaff, the sieve is reciprocated back and forth in the longitudinal direction of the combine harvester.
The sieve apertures are adjusted by one or more rearwardly projecting arms at the rear end of the sieve and these are moved manually by the operator standing at the rear of the sieve, the arms moving transversely of the sieve in a generally horizontal plane.
It has been a long standing problem that the adjustment of the sieve is difficult due to the fact the arms are located on the sieve thus requiring the operator to move to the position at the arms and to stand at the position generally while the combine harvester is operating so that there is dust and debris in the area of the adjustment while the adjustment is effected.
In addition there is a tendency for the adjustment to slip so the adjustment is not properly maintained.
These difficulties have lead to a situation where for many years the adjustment of the sieve has been generally ineffective leading to loss of grain. In the preferred condition, the sieve is adjusted on a regular bases depending upon the conditions which can very during a working shift.
One example of a device for adjusting the sieve is shown in U.S. Pat. No. 4,897,072 of Bestland issued Jan. 30th 1990 in which a relatively complex linkage extends from the arms of the sieve to an adjustment member located in the cab. This device has been available in the market place for some years but has not achieved significant success in that many combine harvesters still operate without such a device. The complexity and expense has to some extent detracted from the use of this device. A motorized adjustment arrangement is also available which includes a motor mounted on the side wall which drives a rod longitudinally to effect the adjustment movement. This device is again relatively expensive and has not been widely adopted. In addition there is no visual indication as to the position of the adjustment.